The abdominal aorta is prone to aneurysmal dilation between the renal and iliac arteries. The attenuated wall of the aneurysm is unable to withstand arterial pressures so that dilation tends to progress to a point where rupture is likely. The highly invasive procedure necessary for conventional repair of an aortic aneurysm consists of an abdominal incision, dissection of the arteries, and the interruption of blood flow to the lower body and legs while an artificial graft is implanted to bypass the aneurysm.
Such invasive surgical repair of vital lumens has profound undesirable effects on the respiratory and cardiovascular systems of elderly patients who typically require the operation. The operation is expensive and entails significant life threatening risk. It is therefore highly desirable to replace conventional surgical repair with a less traumatic, less complicated and safer procedure. The present invention serves these needs, and is particularly well adapted to reconstruction of an abdominal aortic aneurysm. The prosthetic graft of this invention will provide a resilient conduit, bridging the aneurysm and reducing the risk of rupture, without the attendant morbidity and expense of conventional surgical repair. The invention, however, is not limited to aortic aneurysm repair and has applications in a variety of situations in which corporeal lumen repair is required.
There are several devices already existing which are stated to be useful for the remote repair of corporeal lumens. U.S. Pat. No. 4,512,338, issued to Balko et al., discloses a device for transluminal repair of, and restoring patency of, a weakened or damaged corporeal vessel. The device consists of a nitinol wire, previously memory-shaped into a longitudinal coil, which is cooled and reformed into a straight wire and inserted into the vessel requiring repair. When placed in the body and stripped of heat insulating means, the wire warms and returns to its preselected coiled dimensions to support the vessel wall. Use of a device such as nitinol wire may be undesirable because there is a danger of possibly puncturing or lacerating the lumen wall during the emplacement process. Another problem lies in fitting the prostheses to the vessel because the prosthesis does not assume its final shape (and length) until it is inside the artery. The exact position of both ends of the prostheses is very important due to the proximity of vital arteries to the ends of the aneurysm. Yet another problem with these devices is the difficult task of attaching the sleeve to the wire support because the wire is many times longer than the sleeve at the time it is inserted.
U.S. Pat. No. 4,140,126, issued to Choudhury, discloses a device for repairing an aneurysm. The device is mounted on the outside of a carrier catheter, and is positioned in the vessel in a collapsed form, smaller in diameter than that of the vessel. The device is then expanded onto the vessel wall by means of a mechanical expanding apparatus which is controlled by the user from outside the body by means of a wire. Upon expansion, anchoring pins are driven into the vessel wall. The wire is positioned on the outside of the carrier catheter, and is held in place by passing through many slip rings, each of which is firmly attached to the catheter. The slip rings permit the wire to slide when remotely operated. The wire is also attached to the expanding means at its proximal (downstream) end by slip couplings which permit the wire and expansion means to pass through the couplings during the expansion process. This device is mechanically complex and may not apply sufficient force to drive the pins into an atherosclerotic aorta or seal the graft to the arterial lumen. Furthermore, there is nothing to shield the vessel wall from the sharp pins while the device is moving from the insertion point to the point of repair. The pins are interspaced in folds of the graft material and could protrude from these folds while the device is moved into position. This could result in damage to the vessel wall in locations remote from the repair.
U.S. Pat. No. 4,787,899, issued to Lazarus, describes a system of positioning a graft within a body lumen. The graft is loaded into a guide which is inserted into the lumen. An inflatable balloon is used to anchor the distal (upstream) end of the graft onto the wall of the lumen, and then the guide is pushed upstream, pulling the folded graft out of the guide and onto the wall of the lumen, where staples at the proximal (downstream) end anchor into the wall of the lumen. Because the graft is folded or crimped axially, there is no sure method of determining where the expanded graft will position itself on the wall of the lumen, other than by measuring from the point of initial contact on the wall. This is difficult to do utilizing the remote insertion procedure. Also, the balloon providing the anchor for the distal (upstream) end of the graft while the guide is moved upstream may not provide enough pressure on the wall of the vessel to prevent slippage which could result in misplacement of the graft. The axial crimping used in these grafts may not impart radial elasticity and standard graft materials may not have sufficient elasticity as an intrinsic property. The small amount of apparent elasticity present in knitted grafts is actually a form of deformability in that expansion in one direction is accompanied by contraction in another. This means that the "guide" should be very close in size to the lumen of the vessel. As such, it should be introduced directly into the vessel to be repaired, rather than via a distant (much smaller) vessel. Also, the large guide may be difficult to withdraw through the graft after placement since it presents an open edge which might catch on any irregularities of the lumen.
The report, Percutaneously Placed Endovascular Grafts for Aortic Aneurysms: Feasibility Study, from the Department of Diagnostic Radiology, University of Texas M.D. Anderson Cancer Center, printed in 170 Radiology 1033-37 (1989), deals with a self-expanding graft consisting of several stents connected in a chain. Two stainless steel struts run down the length of the chain, forming a rigid structure along the longitudinal axis. The structure is partially covered in a secured nylon sheath, is compressed radially, and is introduced into a lumen via a catheter and a blunt-tipped introducer wire used to push the graft up the catheter and into position. Placement is secured by withdrawing the catheter while holding the introducer wire stationary. This device may be difficult to insert because a chain structure is difficult to push unless it is rigid. The rigidity would make it very difficult to negotiate femoral and iliac arteries which are frequently tortuous. Precise positioning of the graft could be impaired because the pusher wire is not attached to the graft. This poses the potential for mispositioning of the graft during the withdrawal of the sheath. Hemorrhage could also be a major problem with this method of introduction. The introducer sheath is carried into position on the outside of a dilator, which must be removed before the graft can be inserted, leaving the sheath as a conduit from the artery to the outside of the body. The need to introduce the graft complicates the use of hemostatic seals on the sheath. Only one of these grafts carried barbs. The other model showed a tendency to migrate. There is a possibility that the sheathed wall of the barbed device could be breached by the barbs during transfer of the graft to the point of repair because the graft is pushed though the entire length of the catheter with the springs expanded against the inner wall of the catheter. Also, the wide mesh of the material used may not form a barrier to blood leaks, so that the aneurysm could be exposed to arterial pressure.
Endovascular repair of abdominal aortic aneurysm avoids much of the morbidity and mortality associated with conventional surgery. Most patients with abdominal aortic aneurysm lack a segment of non-dilated aorta suitable for attachment of the down stream (caudal) end of a straight (single-lumen) endovascular graft. In these patients a more secure outflow is provided by attaching the two caudal ends of a bifurcated graft to the iliac arteries.
The caudal ends of bifurcated grafts cannot extend to the sites of arterial access in the groin without impairing internal iliac arterial flow, which is an important source of spinal and colonic perfusion after aortic aneurysm repair. Therefore, direct control of the caudal ends of bifurcated grafts is not possible, resulting in a tendency to kinking, twisting and displacement, all of which have complicated previous attempts to apply this approach. The devices and techniques described below provide a means of accurate, hemostatic and permanent insertion of a bifurcated graft, with provision for the prevention of correction of these potential complications.